Hey Aggie,
I'll tell you a little bit more about that shutter. It is a LUC shutter, kind of like a packard shutter, but round and uses a standard cable release. It is dial set like the old compur shutters and has 3 settings. Bulb, a shutter speed of about 1/15 sec, and open-for focusing. It fits on the outside of a lens with a diameter of between about 40mm and 52mm by 3 adjustable set screws. I use it on what I think was originally and enlarger lens. It is a 135mm Hermagis Anastigmat Hellor. It is uncoated, has some bubbles in the glass, and has a slight haze. Not what I would want to use for enlarging, but is great for portraits. I haven't shot anything with a modern enlarging lens, but am planning to soon.